The invention relates to a process for the cultivation of matrix-bound biologic cell systems, such as bacteria, fungi, mammalian cells and the like, on microcarrier particles that are selectively displaced within a replenishable nutrient medium in a confined area to provide for uniform exposure of the cell systems to available nutrient material.
As is known, the cultivation of matrix-bound biologic cell systems may conveniently take place (for example, see Lewis et al.: 2nd Gen. Meeting ESACT, June 23-26, 1978 or Levine et al.: Somatic Cell Genetics 3(2):149-155, 1976) on microcarriers in the form of carrier particles having a specific gravity close to the reference magnitude of 1 g/cm.sup.3, e.g. gel beads, suspended in a nutrient medium forming an environmental atmosphere suitable for the fermentation of the culture in each case. For a uniform supplying of the culture with nutrient substrates and oxygen, such suspension is contained in a culture vessel and displaced during the fermentation either by displacement of the culture vessel or by displacement of the contained suspension by means of internal mixing elements, by a back-and-forth or rotating movement. An attempt is thereby made to apply the nutrient solution and the oxygen as uniformly as possible to the culture that is spreading on the surfaces of the microcarriers. Such known process for the cultivation of matrix-bound cell systems on microcarriers freely suspended in a nutrient medium is generally employed at the present time despite its disadvantages or deficiencies as hereafter pointed out.
Thus where the suspension is directly kept in motion by mechanical mixing elements, for example by magnetic agitators, perforated disks moving back and forth, or the like, an abrasion or shearing of cells of the culture spreading on the surface of the microcarriers is unavoidable. The magnitude of the shearing forces is generally proportional to the intensity of the agitation. Such shearing forces however not only act disadvantageously on the culture but cause electrostatic charges to develop in the system, as well as inducing foaming of the protein-containing nutrient medium when the culture is supplied with oxygen at the same time. Additionally, the supplying of the cells with nutrient materials is also thereby impaired. Even if great care is taken, it is scarcely possible to avoid the entry of foreign substances into the suspension with the use of such mixing elements, so that the sterility of the culture is no longer assured.
It is apparent that these mechanical mixing disadvantages may be partly avoided if such direct contact mechanical mixing elements are dispensed with and, as known, the culture vessel is put into a rolling or back-and-forth movement. However, a disadvantage which then arises in this case is that in such one-or two-dimensional movements, the microcarriers do not get to float and thereby loosen away from the vessel walls; that is they always remain in the lowest level of the vessel, even though their motion is a "rolling" one. A reciprocal contact here, too, leads to abrasion of the cultures; in addition, a uniform supplying of the cultures with the nutrient medium and with oxygen is no longer assured under these conditions.